Coders and decoders for pulse code modulation systems



Dec. 18, 1962 A. E. BREWSTER 3,

commas AND DECODERS FOR PULSE com: MODULATION SYSTEMS Filed Feb. 25, 1960 Inventor A E BRA-W575i? we who WW United States Patent 3,069,641 CODERS AND DECODERS FOR PULSE CODE MODULATION SYSTEMS Arthur Edward Brewster, London, England, assignor to International Standard Electric Corporation, New York, NY.

Filed Feb. 23, 1960, Ser. No. 10,501 Ciaims priority, application Great Britain Feb. 26, 1959 4 Claims. (Cl. 336-455) ,rial have been proposed, in which one core is provided for each signal level to be represented. In order that the signal waves may be reproduced with sufficient fidelity, a relatively large number of levels must be provided for, and the winding and assembly of the corresponding cores becomes rather an expensive matter, and is not easily adaptable for an automatic process.

The cores have hitherto usually been made from a suitable ferrite material, and the ferrite materials available at present place limitations on the switching speed, and the hysteresis loss is generally inconveniently large. Certain metallic materials, such as Permalloy, are in principle more advantageous in these respects, but if the advantages are to be obtained, the corresponding cores would need to be impracticably small, and this would increase the difliculties associated with applying the windmgs.

The object of the invention, therefore, is to provide an alternative assembly for a magnetic core device, which could, for example, be used in a pulse coder or decoder, and which is suitable for manufacture by an automatic process and which also enables metallic magnetic materials to be used instead of ferrite materials.

This object is achieved according to the invention by providing a magnetic core device comprising a toroid formed by a closely wound spiral of magnetic tape, and a winding for carrying a current, a turn of which winding passes between two of the turns of the spiral.

The invention will be described with reference to the figures of the accompanying drawing in which:

FIG. 1 shows a plan view of an embodiment of the invention; and

FIGS. 2 and 3 respectively show side views .at sections of FIG. 1.

The electrical advantage of using Permalloy, or other similar alloys, for the magnetic material for the magnetic cores of a coder is only obtained if the Permalloy is very thin, either in the form of thin tape, or of deposited coatings. It is well known in the art to make a toroidal core by closely winding a fiat spiral of Permalloy tape. The embodiment of the invention shown in FIG. 1 comprises such a wound spiral 1, though the turns are shown widely separated for clearness. This embodiment also comprises a number of windings for producing the equivalent of the core assembly which determines the quantising amplitude levels in a pulse coder described, for example, in the specification of co-pending application Serial No. 819,089, filed June 9, 1959, and assigned to the same assignee as is this application. This core assembly comprises 70 separate magnetic cores, and each core has a sampling winding, a signal wave winding, a bias winding, and several output digit pulse windings. The winding of such a core assembly is a very intricate operation which has to be done by hand.

In FIG. 1, each turn of the spiral winding 1 at the sampling winding, and 3, which is the signal wave winding. These two windings .are both shown with two turns, and oppositely wound, but each may in practice have 1 or any other suitable number of turns, and both may be wound in the same direction.

7 At the right-hand side of FIG. 1 there is shown a bias winding 4, the turns of which link different numbers of turns of the spiral, and so must pass between these turns as indicated. Likewise four output digit windings 5, 6, 7 and 8 are also shown, but it will be understood that there may be more or less than four such digit windings. Each digit winding will link only certain of the turns of the spiral.

FIGS. 2 and 3 show side views at sections of FIG. 1 to indicate how the windings are wound. They are only diagrammatic, and are not regular sectional views. FIG. 2 is taken in the neighbourhood of the windings 2 and 4 and FIG. 3 in the neighbourhood of the windings 3 and 5 to 8. From FIG. 2 it will be seen that the sampling winding 2 is an ordinary winding linking all the turns of the spiral 1, while successive turns of the bias winding link 1, 2, 3, etc., turns of the spiral. The reason for this is that the bias fields required for successive turns of the spiral increase proportionally to the numbers 1, 2, 3, 4, etc. It will be clear that if a given bias current be passed through the winding 4, the innermost turn of the spiral will be linked by all the turns of the bias winding and so will have the maximum bias field, while the outermost turn of the spiral is linked by only one turn of the bias winding 4 and will have the minimum bias field.

On the left-hand side of FIG. 3 is shown the signal winding 3 which links all the turns of the spiral in the same way as the samping winding 2. At the righthand side of FIG. 3 is shown only the digit winding 7. This is shown as linking the first two turns of the spiral (counting from the inside) and the fifth turn. This winding may also link certain of the other turns of the spiral which are not shown in FIG. 1. Which turns are linked will be determined by the code pattern. All the other digit windings will be applied in the manner shown for digit winding 7, but will link other combinations of the turns of the spiral. Thus winding 5 links turn 1 of the spiral; winding 6 links turns 1, 3 and 5 of the spiral, and winding 8 links turns 2, 3, and 4. These windings may also link other turns of the spiral not shown.

The bias and digit windings will preferably be applied during the winding of the spiral, which will be done on a central mandrel (not shown). The windings are put in position whiie the spiral is being wound: thus aftereach turn of the spiral has been wound, one turn of the bias winding is taken round through the centre (for example through a suitable horizontal slot in the mandrel), and a wire for each digit winding which should link the turn is put in position. Then the next turn of the spiral is wound, and the appropriate windings are put in place, and so on.

After the bias and digit windings have been put on, the sampling and signal wave windings 2 and 3 are wound on the complete core in the usual way.

These windings processes can be carried out auto matically by a machine in which the known techniques of toroidal winding, and weaving, are suitably combined. It will be seen that the interleaving of the turns of the space .21

Q.) spiral by the bias and digit winding wires is quite similar to a weaving process.

It be desirable to use a thin ring (not shown) of suitable non-magnetic material as a foundation on which the spiral is wound. it is also desirable to begin the first turn of the spiral at a point 9 near the position where the digit and bias windings are to be applied so that the longest possible are of contact between the first and second turns is obtained before the first turn is linked by any windings. Alternatively, two or three turns of the spiral may be put on as a foundation before any interleaving occurs, in which case the said two or three turns may be treated as constituting the first turn of the spiral, as far as the bias and digit windings are concerned.

It will be understood that the spiral should be as tightly wound as possible so that the turns will be in contact throughout the major portion of the circle. The effect of the interleaving of the windings is to divide the magnctic circuit locally into a number of parallel magnetic circuits each of which can be separately biassed and triggered, and thus each of them corresponds to one of the cores of the previously proposed arrangement mentioned above. The magnetic circuits of the outer turns are, of course, longer than those of the inner turns. The extreme range of length can, for example, be of the order of 2:1. It the magnetic circuits are triggered by using sampling pulses of specified flux linkage as described in aforesaid copending application, No. 819,089, this difference in magnetic path length is of small consequence. The longer magnetic circuits will require larger currents to trigger them but these larger currents will be available if such sampling pulses are used.

While the arrangement shown in FIG. 1 can provide for 70 levels, for example, in case it is desired to code a signal wave having 35 positive and 35 negative levels, then it is preferable to use two arrangements according to FIG. 1, each designed for 35 levels, and they would then be oppositely biassed.

The assembly shown in FIG. 1 should be as small as is practicable in order to minimise the hysteresis losses. For example, the core could have an internal diameter of 0.25 inch, and could be wound with suitable Permailoy tape (1.0005 inch 6.1 inch w de, and the wire used for the elled copper wire (diameter {2.0924 inch). Then the maximum magnetic path length would be about 1.6 times the maximum path length in the case of a core which provides for 35 levels.

The windings could alternatively be wound with thin insulated copper tape instead of copper wire.

While Permalloy is suggested above as the material for the magnetic tape, it will be understood that other magnetic metals or alloys having suitable magnetic characteristics, and capable of being produced in the form of thin tape, could be used.

it will be evident that since a decoder employing magnetic cores has digit and other windings similar to those of a coder, the arrangement of FIG. 1 can be adapted for a decoder by applying and interleaving the required rindings in the manner described.

gs could be 46 SWG en am- Furthermore, the type of construction illustrated in FIG. 1 can be used for other applications besides pulse coders and decoders. A device called a transfluxor, used for information storage, comprises a solid toroidal core of ferromagnetic material through the material of which one or more small holes are provided parallel to the axis of the toroid, by means of which holes the magnetic circuit of the toroid is divided into two or more parallel magnetic circuits. Windings are threaded through the small hol s which do not pass through the centre of the toroid. It will be evident to those skilled in the art that the equivalent of a transfiuXor may be produced by the device shown in FIG. 1 by interleaving suitable windings with the turns of the spiral, and the arrangement can provide a much larger number of parallel magnetic circuits than would be practicable with a transfluxor in its ordinary form.

Whilethe principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What I claim is:

l. A magnetic core device for use in an electric pulse coder or decoder, comprising a close'y wound spiral of magnetic tape forming a flat toroidal disc, a plurality of digit windings each of which comprises a conductor which passes between certain adjacent turns of the spiral in such manner that each digit winding effectively links only predetermined turns of the spiral, the predetermined turns of the spiral which are linked being different for each digit winding, a bias winding having a plurality of turns and consisting of a conductor which is inteleaved with the turns of the spiral in such manner that different turns of the bias winding effectively link respectively different numbers of turns of the spiral, and two further windings each of which links all the turns of the spiral.

2. A magnetic device comprising:

a toroidal core consisting of a plurality of closely wound turns of magnetic tape; and

a winding consisting of at least three coils connected in series, each coil linking a different number of adjacent turns of said toroidal core.

3. A device according to caim 2 comprising a further winding for carrying a current, and having a plurality of turns interleaved with the turns of said toroidal core in such manner that different turns of the said further winding effectively link respectively diiferent numbers of turns of said toroidal core.

4-. A device according to claim 2 comprising an addi tional winding for carrying a current, which additional winding links all the turns of said toroidal core.

References Cited in the file of this patent UNITED STATES PATENTS 

